Vapor vent for floating roof tanks



June 24, 1952 F. D. MOYER 2,501,317

VAPOR VENT FOR FLOATING ROOF TANKS Filed June 26, 1946 j zza PatentedJune 24, 1952 VAPUR VENT FOR FLOATING ROOF TANKS Frederick D. Meyer,Chicago, 111., assignor to Chicago Bridge & Iron Company, a corporationof Illinois Application June 26, 1946, Serial No. 679 382 Claims. 1

This invention relates to a vapor venting means for a floating rooftank.

Floating roof tanks include a shell 'for holding the storedliquid and aroof that floats on top of the liquid. Sealing means are providedbetween the roof and the shell of the tank to prevent contamination ofthe stored liquid and to reduce evaporation'losses. When the tanks areused for storing volatile liquids, vapor forms under the roof. When thisvaporhas accumulated in relatively large quantities it is necessary thatit be vented to the atmosphere. The present invention relates to animproved venting means permitting the escape of the vapor whether asformed or when a, predetermined pressure has been reached in the vaporspace.

The invention includes broadly a vapor venting means comprising aprimary vapor space located above the surface of the stored liquid, asecondary vapor space separate from the primary vapor space,communicating means connecting the two vapor spaces, vent means in thesecondary vapor space at a, point remote from the communicating means,means for maintaining a higher pressure in the primary vapor space thanin the secondary vapor space during venting, and means for returningcondensed liquid from the vapor to the stored liquid. In a preferredform there is provided a downwardly extending barrier around the roofadjacent the edge thereof and extending down into the liquid, so thatthe primary vapor space-will be located within the confines of thebarrier and beneath the floating roof. The secondary vapor space is thenbetween the barrierand the edge of the roof-and the shell of the tank. Apassageway is provided through the barrier so that vapor may escape fromthe primary vapor space into the secondary vaporspace. A vent open tothe atmosphere is provided in the secondary vapor space at a pointremote from-the passageway. If :lt is desired to vent the vapor onlywhen a predetermined vapor pressure has been reached in the primaryvapor space, the inner end of the passageway may be arranged so as to beimmersed in the liquid until this predetermined pressure has beenreached.

JIn-the ordinary floatingroofs where the shsell is'substantiallycylindrical and the roof is substantially circular the vent openin totheatmospherecan be located 180 from the passageway. Vapor flowing throughthepassageway intofthe:secondary vapor space-will then flow in opposite'directions'around the' tank to the vent. During this travel liquid:will. condense from the vapor andiall into the stored liquid betweenthe barrier and the shell of the tank. When the vapor flows from therelatively high. pressure primary vapor space into the low pressuresecondary vapor'space a refrigerating action will'be caused by theexpansion of the gas. This-refrigcrating action aids in condensing someof the vapor, and this condensed liquid will fall by gravity into thestored liquid.

The invention may be used oneither a single deck roof or a double deckroof, and the venting means may be caused to operate either at apredetermined vapor pressure or asvsoon as any vapor is formed. When theinventionis used on a single deck roof the barrier separating theprimary and the secondary vapor spaces may be an annular pontoon aroundthe edge of the roof. When the invention is used on a-double deck roofwherein the roof itself acts as a pontoon the barrier may be a dependingcylindrical plate, either arranged adjacent to the roof or spacedinwardly from the edge of the roof.

The invention will be described as related to the embodiment shown inthe accompanying drawings. Of the drawings Fig. 1 is a plan view of afloating roof tank embodying the'invention, and Fig. 2 is averticalsection taken along line 2-2 of Fig. 1.

In the embodiment shown in the drawingsthe floating roof tank comprisesa shell ill and a single deck floating roof H therein. Thereof is lowerat the center than at its edge and isprovided with a depending annularpontoon l2. In the center the roof there is provided acylindricalpontoon i3 arrangedon top of the roof so that it will be immersed in;any rain water that collects on top of the roof. This centralpontcongives added buoyancyto theroof when under a load of water. ;Incontact-withthe inner surface of the shellof thetanktherevislocated-theordirn ry flat sealingm mber iflw upp ted-from th roof inanydesiredymanner. ,A flexible sealing member extends; fromgthe edge ofthereof to the top of the flat sealing member 14 and is usuallyafabricimpregnated witha flexibleirnpervious material.

Ar pe it extends throu h one porti n o th annular pontoon l2, and thispipe hasitsinner end lower than its outer end so that the inner end willordinarily be'imrnersed in the-stored iquid ii. A ventl8 openin t the amospher is located substantially around the roof from the pipe 1'6.

When vapor is formed in the tank it Will -col,- lect intheprimary vaporspace H) under the deck of the floating roof and within the confines ofthe annular pontoon l2. The secondary vapor 7 space 20 is locatedbetween the annular pontoon I2 and the shell IE! of the tank. As theflat sealing member I4 contacts the shell of the tank the secondaryvapor space is actually between the annularpontoon I2, the flat sealingmember I4, and the flexible sealing member I5.

When suflicient vapor has accumulated in the primary vapor space I9 toraise the roof so that the inner end of the pipe I6 is exposed, vaporwill escape from the primary vapor space I9 through the pipe I5 into thesecondary vapor space 28, and will then flow in opposite directionsaround the roof and escape through the vent It. A baffle plate 2| isprovided opposite the outer end of the pipe I6, and this plate will aidin condensing liquid from the vapors.

As the pressure within the primary vapor space I9 is greater than thatwithin the secondary vapor space 20, the vapor flowing through the pipeI6 and into the secondary vapor space will expand, and this expansionproduces a cooling efiect on the vapors. While the vapor is flowingthrough the secondary vapor space to the vent [8, much of the vapor willcondense, and the resulting liquid will fall by gravity into the storedliquid that is between the annular pontoon I2 and the flat sealingmember I4. When suflicient vapor has escaped from the primary vaporspace I9 to materially lower the pressure within the primary vaporspace, the annular pontoon I2 will sink back into the liquid until theinner end of the pipe is i immersed in the liquid. No more vapor willflow until the pressure has been again increased to a predeterminedvalue.

Having described my invention as related to the embodiment set out inthe accompanying drawings, it is my intention that the invention be notlimited by the details of description unless otherwise specified, but irather be construed broadly within its spirit and scope as set out inthe accompanying claims.

I claim:

1. In a floating roof tank comprising a shell adapted to store liquidand a floating roof there in having its peripheral edge spaced from theshell, an annular barrier extendin downwardly from the roof forming aprimary confined vapor space located above the surface of the storedliquid inside the barrier, and a secondary confined vapor space locatedabove the surface of the stored liquid and outside the barrier separatefrom the primary vapor space, communicating means connecting the twovapor spaces and being normally closed by the stored liquid, a vent pipemeans in the secondary vapor space at a point remote from thecommunicating means, said communicating means being so arranged that ahigher pressure is required in theprimary vapor space than in thesecondary vapor space during venting.

2. The vapor venting means of claim 1 wherein the communicating meansremains closed by the stored liquid until a predetermined pressure hasbeen reached in the primary vapor space.

3. The Vapor venting means of claim 1 wherein the secondary vapor spaceis above the liquid surface between the edge of the roof and the shell.

4; The vapor venting means of claim 1 wherein the Primary vapor space isbeneath the roof and the secondary vapor space is above the liquidsurface and between the edge of the roof and the shell.

5. In a floating roof tank comprising a substantially cylindrical shelladapted to store liquid, a substantially circular floating roof thereonand a flexible seal between the roof and the shell, said roof having adownwardly extending annular barrier forming a primary confined vaporspace located beneath the roof and above the surface of the storedliquid and a secondary confined vapor space located above the liquid andbeneath the flexible seal between the floating roof and the shell,communicating means normally closed by the stored liquid and connectingthe two vapor spaces, and a vent pipe means in the secondary vapor spaceat a point substantially from the communicating means.

6. The vapor venting means of claim 5 wherein the barrier extends aroundthe edge of the roof and downwardly into the stored liquid with theprimary vapor space being within the confines of said barrier.

7. The vapor venting means of claim 5 wherein the barrier extend aroundthe edge of the roof and downwardly into the stored liquid with theprimary vapor space being within the confines of said barrier, and thesecondary vapor space being between the barrier and the shell of thetank.

8. The vapor venting means of claim 5 wherein the barrier extends aroundthe edge of the roof and downwardly into the stored liquid with theprimary vapor space being within the confines of said barrier, and withthe communicating means extending through said barrier.

9. The vapor venting means of claim 5 wherein the communicating meanscomprises a passageway with the end of the passageway adjacent theprimary vapor space being immersed in the stored liquid until apredetermined pressure has been reached in said primary vapor space.

10. In a floating roof tank comprising a substantially cylindrical shelladapted to store liquid, a substantially circular floating roof thereinand a flexible seal between the roof and the shell, a barrier around theedge of the roof and extending downwardly into the stored liquid forminga primary vapor space under the roof located within the confines of saidbarrier and above the surface of the stored liquid and a secondary vaporspace at the edge of the roof beneath the flexible seal between thebarrier and the shell of the tank and above the surface of the storedliquid, a pipe connecting the two vapor spaces, and a vent opening fromthe secondary vapor space and located substantially 180 from thepassageway.

11. The vapor venting means of claim 10 wherein the barrier is anannular pontoon located beneath the roof.

12. The vapor venting means of claim 10 wherein the barrier is anannular pontoon located beneath the roof and the pipe extends throughthe pontoon, the inner end of the pipe being under the liquid surfaceuntil a predetermined pressure has been reached in the primary vaporspace.

13. In a floating roof for a liquid storage tank including flexiblesealing means between the roof and the side walls of the tank and saidroof having an outer annular pontoon adapted to be immersed in thestored liquid, said pontoon defining an inner vapor space above thestored liquid and beneath the roof and said pontoon defining an outervapor space above the stored liquid and beneath the sealing means, meansfor permitting escape of air from the inner vapor space when liquid isbeing introduced into said tank and for permitting entrance of air intothe inner vapor space when said tank is being drained, during thatperiod of filling or draining when the roof is resting on the bottom ofthe tank, comprising a first vent extending diagonally upwardly andoutwardly through the pontoon and communicating with said vapor spaces,a second vent communicating with the outer vapor space and theatmosphere, the inner end of said first vent being so positioned as tobe immersed in the stored liquid when the roof is floating therein.

14. Vent means for a floating roof tank having a floating roof having adeck and an outer annular pontoon defining a vapor space inside thepontoon beneath the deck and a separate confined space outside thepontoon comprising a vent extending through the pontoon and having aninner end opening to the space inside the pontoon and normally immersedin the liqannular pontoon defining a vapor space inside the pontoonbeneath the deck and a separate confined space outside the pontooncomprising a vent extending downwardly through the pontoon and havingone end opening through the inner side wall of the pontoon at a pointbelow the normal liquid level whereby said end is normally immersed inthe liquid in the tank and adapted to be relatively raised above thelevel of the liquid with relative upward movement of the pontoon inresponse to increasing pressure in said vapor space, the other end ofsaid vent opening through the outer side wall of the pontoon, and meansconnecting the space outside the pontoon with the atmosphere.

FREDERICK D. MOYER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,545,352 Rodriguez July 7, 19251,653,387 Brown Dec. 20, 1927 1,904,339 Wiggins Apr. 18, 1933 FOREIGNPATENTS Number Country Date 38,851 Netherlands July 17, 1936

1. IN A FLOATING ROOF TANK COMPRISING A SHELL ADAPTED TO STORE LIQUIDAND A FLOATING ROOF THEREIN HAVING ITS PERIPHERAL EDGE SPACED FROM THESHELL, AN ANNULAR BARRIER EXTENDING DOWNWARDLY FROM THE ROOF FORMING APRIMARY CONFINED VAPOR SPACE LOCATED ABOVE THE SURFACE OF THE STOREDLIQUID INSIDE THE BARRIER, AND A SECONDARY CONFINED VAPOR SPACE LOCATEDABOVE THE SURFACE OF THE STORED LIQUID AND OUTSIDE THE BARRIER SEPARATEFROM THE PRIMARY VAPOR SPACE, COMMUNICATING MEANS CONNECTING THE TWOVAPOR SPACES AND BEING NORMALLY CLOSED BY THE STORED LIQUID, A VENT PIPEMEANS IN THE SECONDARY VAPOR SPACE AT A POINT REMOTE FROM THECOMMUNICATING MEANS, SAID COMMUNICATING MEANS BEING SO ARRANGED THAT AHIGHER PRESSURE IS REQUIRED IN THE PRIMARY VAPOR SPACE THAN IN THESECONDARY VAPOR SPACE DURING VENTING.